# The Space Hose

by gutemine
Tags: hose, space
P: 15,294
 Quote by gutemine gutemine is actually a character from the Asterix comics book (I think in English she is called Impedimenta
Ah Impedimenta, yes. I remember her.

Always had a thing for Panacea myself...
 P: 59 Obelix has the same problem - so you are excused. But Buzz is definitely the better Character for illustrating this concept - may the Toys (and Pixair) forgive me.
 P: 3 It's obvious that this theory has some flaw in it. All the "space elevator" concepts out there depend on one thing, a rigid wire which is held in orbit by a large mass. This large mass is critical because it holds the string taught. Let's assume for a second that your idea works and you get the thing airborne and completely upright (this alone is very unlikely for reasons that I will describe later). So now you have a tube which is slightly fluttering around in the air (because remember you chose TURBULENT airflow. This is why your wild wacky inflatable tube man flutters in the air instead of standing straight like you would like him to, it's because of the turbulent flow. If wild wacky inflatable tube man were using a high viscosity fluid such as water, he would not dance because of the LAMINAR reynolds number). But i'll be nice. Let's assume that you figure out a way to get the thing stable and upright, I donno you inject some laminarizing particles... or something... But anyway it's straight, it's upright and it's stable. So now you look up at the top of your glorious hose and you realize it's curving... but how can this be? There's such a mighty air pressure! It's for the same reason that poster #4 said. You must impart SIDEWAYS velocity. Vertical velocity just doesn't cut it. Imagine you attach a string to a frisbee and throw it, that string is going to twist with the frisbee. That's because the tension and centrfugal force, and the sideways strength of the fibers in the string just cannot overcome the change in angular velocity. If you had a big steel rod and you spun it, it would STILL BEND (a little bit, but imagine that big steel rod is 80,000 ft long and you get the idea). Ok so let's assume that you get the thing upright, stable, and you somehow reinforce it so that it's not bending under its own weight (I have no idea how you're going to do this, but let's assume you get it to not bend). So now you're like OMG I just erected a huge tube, what a glorious monument to my awesomeness!!!!! So then you try to blow a small satellite up your tube. You stick it in the bottom and start blowing. You notice that as soon as it's about 100 ft above the ground that your perfectly straight tube begins to bend again, but in a V bend (because we assumed that your tube was erect under its own weight). So now ur like ok I'll just increase the air pressure (at which point I guarantee you will blow a hole in whatever material you are using, even CNT's). The core problem with your space hose is connected to the conservation of angular momentum. You cannot simply send an object into a state of higher angular momentum without robbing that angular momentum from something else. That's what the big rock at the top of the space elevator does. We have to capture an asteroid with a lot of angular momentum so that we can slowly impart its momentum to the satellites we send up there. The elevator cable doesn't work like a normal elevator cable, it must strain SIDEWAYS. The upward force is TRIVIAL compared to the sideways force that must be imparted by the cable on the satellite. This is why the vast majority of a rocket's flight is on its side and not upright.
 P: 15,294 Despite z06_pit's heavy sarcasm, he has a point. He's touched on something that's been bothering me too. Even with the space elevator, by the time you reach GEO, you are moving at a substantial velocity around the Earth (orbital velocity, in fact). This transverse velocity does not come free. As he says, it must be imparted upon the rising payload. In the space hose, you don't have that rigid structure's ability to impart transverse velocity on its payload. You'll have to account for that.
 P: 3,390 I have to say, Z06_Plt post is one of the best in this thread. I think the sarcasm is somewhat heavy, but necessary in so far as it reinforces the critical points which cannot be avoided and really do need addressing at this early stage. Solving one problem at a time may seem like a good idea, but without forward planning it can mean you end up back tracking and having to perform multiple redesigns (which can be costly and time consuming).
P: 15,294
 Quote by Z06_Plt So then you try to blow a small satellite up your tube. You stick it in the bottom and start blowing. You notice that as soon as it's about 100 ft above the ground that your perfectly straight tube begins to bend again, but in a V bend (because we assumed that your tube was erect under its own weight). So now ur like ok I'll just increase the air pressure (at which point I guarantee you will blow a hole in whatever material you are using, even CNT's).
On the other hand, let's keep in mind that the satellite only weighs 9g (yes, nine grams). That's a pretty negligible amount of mass to toss about.

The N-prize rules are simple deliberately. Scaling challenges are pointedly outside the scope of this project.
 P: 59 If the relationship N-SAT size to hose diameter is less then something like 10 there should not be a real problem - it will simply move to the center of the flow where the highest speed occures. And even when it would touch the walls, the force of a tangential impact is small and a hose under surpressure is almost perfect elastic. It would maybe mage some strange drumm sound while beeing blown upwards. Or we make it intentionally tach the wall with a kind of parachute with holes. But the blowup behaviour of the SAT and the impact of turbulent flow is something relatively easy to test. You would only need to buy a few hundred meter of foil and try it out, Because of the weight of such a hose beeing in the 10kg range a simple model plain propeller and engine could already do all the blowing needed. Somebody volunteering to try it out ? But be aware you would need at least a very simple stabilizing diffusor on top or you will fail erecting it when going beyond a few meters. I think the N-prize rules are pretty clever - they remove some problems and create new ones - but just building a small Saturn V or a small Space Shuttle would be boring, woudln't it ? So I think the lack of scalability is the opportunity of the whole thing. Even for the space hose -10" diameter is peanuts, but more then enough for such an N-SAT. And actually it is exactly this very strange lift/weight/power/strength ratio which seem to make such a hose concept feasable - in the first run targetted at this purpose. Finally if it works at that scale you can try to make a real lift device for more sensemaking purposes. And yes, Paul did this intentionally to force the people on new ground, instead of trying to dig the same old holes all over again. gutemine
 P: 59 As the slides say, rockets are boring, but they work. Unfortunately there is no such string which the rocket could pull - it would first tear from the acceleration and then from its own weight. The whole idea of the hose is to do everything slow and under control. Erecting it in a day, blow with jogging speed (maybe bicycle speed, remember friction goes with v²). Using ultra light material to keep the forces and masses low. As I said at the halfbakery. If you have to build something in the desert - then use SAND! We live at the bottom of an ocean of air - so it is the logic construction material! I just followed this logic to the extreme. Continuously supporting the weight is actually the only real new thing within the whole concept. Instead of using a wing to create lift you simply use friction - as the slides say, the whole thing is a dumb circular flag blown from the inside - which should make it work also in vacuum. PS: The entire problem with ballons running our of steam beyond 30-40km simply annoyed me - you get 1/3 of the 100km almost for free, and then the driver kicks you out of the bus and you have to wait for a rocket ? So I decided to start my own bus/hose :-) And this is also the reason why I dislike the ballon+rocket or even hose/tower+rocket conecepts. If I have air blowing out on the top Bernoulli and de Laval should be everything you need to even get the lacking orbital speed (again for an N-SAT - not for a space shuttle) PPS: My background actually is poor on such things (I have other hobbies too), but I'm using it as good as a can. And as I already said - the math and pyhsics behind this is not something which should not look familiar when you had a good physics teacher at highschool. And so far we did a good job in debugging the concept and analyze its problems or try to get an idea how big they really are. If you solve all small problems usually the big ones are gone too is one of my favoirite sayings. And as the original post says - N-prize is also about the entertaining value - so I don't have a problem if we have fun together. gutemine
P: 3
 Quote by gutemine Unfortunately there is no such string which the rocket could pull - it would first tear from the acceleration and then from its own weight.
Rocket acceleration is less than 3g at all times.

Breaking under its own weight is a different story entirely. However, if you use nylon, this problem gets a lot simpler.

 Quote by gutemine the whole thing is a dumb circular flag blown from the inside - which should make it work also in vacuum.
 Quote by Niel Armstrong Oh **** this circular flag doesn't blow on the moon! I better stick a rigid wire in there for support.
Granted, Col Armstrong is referring to different situation than yours, but I just thought that it was funny, considering your choice of words.

What you described is different than a circular flag, there are many reasons why it is different than a circular flag. The most prominent of which is the fact that a "flag" is generally horizontal, and a "tube" is generally vertical. The second most prominent of which is the fact that when you extend this tube such a distance, the frictional losses prevent air from reaching the other end without manual pumping. This pumping changes the problem from that of friction to that of pressure/structural rigidity.
 P: 15,294 Cool. I'd be interested in your first take on fan speed/pressure.
P: 59
 Quote by DaveC426913 Cool. I'd be interested in your first take on fan speed/pressure.
Well, the first key finding was that actually the blow speed at the bottom is lower (which is logic if you limit the head to 270m/sec which is approximately the speed of sound at -90 degree of Celsius), but you need a slightly higher surpressure to keep the whole thing stable (approximately 500-1000 Pa). This helped a lot to sort out the do I feed flow speed or surpressure at the bottom question which I never could sort out when I tried to calculate from there (predicting these 2 variables at the top is much easier and logically).

Funny is that the top contributes most of the pull forces even without the diffusor, which is good for extra stability. I already assumed this (because of the v² of the friction forces, but I didn't have any idea to what extent)

I'll see if I can warp it up and add some comments and colors for the changabel fields until this evening than you can play with it yourself.

Having such a 'virtual Space Hose' where all the parameters are changeable is pretty funny, and it even gives interesting results like pressure waves on top if the surpressure is too low, or how low you can bring the hose tensions down before it fails to stay errect (approximately 100N/mm² - which is not so far away from plain PE)

As I already mentioned I'm doing also some open source software development as another hobby so as soon as I found the formulars on how to calculate the Standard Atmosphere model from the definitions it was not so diffucult to build a Spreadsheet out of it.

http://www.pdas.com/coesa.ht

Then I found another Webpage where you can calculate air viscosity for all temperatures:

http://www.lmnoeng.com/Flow/GasViscosity.htm

It took me almost 1 hour to get all 100 viscosities for the model, but I was too lazy to try to reverse engineer the math for this too :-)

From these two raw inputs you have everything needed for the pressure loss calculation at all heights, and then the fun started when putting it together.

gutemine
 P: 59 One more question on the wind - I found a nice picture on this (see attachment) Would this mean that a hose with pull from top would actually form more or less such a bent curve ? Because I would like to include also the pull force calculation into the excel, and for this I need a better understanding of the distribution of the wind force on the lower end of the hose. gutemine Attached Thumbnails
 P: 59 Damned - I still have problems with my Excel and the discrete calculation steps because now I have a circular reference. If I go 1km down this means that the pressure on the bottom should be the one at the top + pressure loss from friction + hydrostatic pressure of the 1km of gas. The problem is that hydrostatic pressure is dependant on the density, which is resulting from the pressure from bottom to top (if I asume that temperature is always aproximately outside temperature of the standard atmosphere) = circular reference. Now I understand why the books are saying this is a differetial equation with an integral which is only numericially solveable - if at all :-( And if I try to overcome this by simply taking the previous density as I did until now the result is underestimating pressure, which makes the numbers look good, but then the model is invalid beyond the top few kilometers of the hose, because only there density and hence hydrostatic pressure is low enough to allow such a simplification. So calculating top to bottom was a good idea, but gives wrong results at the bottom because of the discretisation. This is also the reason why going from bottom to top produced too high numbers on top. But problems are there to be solved, and input is welcome ;-) gutemine
 P: 5 Is the "space hose" thread over?

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